1. Field of the Invention
This invention relates to catalysts for expediting the oxidation of an olefin to the corresponding oxirane; and, more particularly to a shaped and metal-bound catalyst of a boron-containing substance for catalyzing the liquid phase epoxidation of olefins with organic hydroperoxides.
2. Statement of the Prior Art
Oxiranes or epoxides, while being valuable commercial products in and of themselves, are also commercially valuable as starting reactants for synthesizing many useful compounds such as polyether polyols for urethane systems. Over the years many methods have been disclosed for synthesizing such compounds. The majority of these methods involves the oxidation of the corresponding olefin. For example, it is known that ethylene can be converted to the corresponding epoxide by a vapor phase partial oxidation with molecular oxygen over a silver catalyst. However, the ease of olefin oxidation varies greatly depending upon the size and structure of the olefinic starting reactant and therefore many of the disclosed processes are not effective for epoxiding olefins in general.
Recently it has been disclosed that olefinically unsaturated organic compounds can be oxidized to the corresponding oxirane compound in liquid phase with organic hydroperoxides in the presence of various catalysts.
Various tungsten catalysts, their preparation and uses are described in Ind. Eng. Chem. 57 (9), 53-60 where the conversion of olefinic double bonds is described as requiring high concentrations of the olefin reactant and of the tungsten catalyst. In particular, the article describes the epoxidation of allyl alcohol in water using 1.2-2.0 allyl alcohol and 15-40 water to 1.0 of hydrogen peroxide, with a catalyst concentration of about 4grams/mole of H.sub.2 O.sub.2 ; these catalysts being tungstic acid, phosphotungstic acid or their salts.
The same article also mentions that suitable tungsten catalysts may be prepared by pelleting tungstic acid with 2% graphite as a lubricant at high pressures of up to 62 tons per square inch.
More recently it has been disclosed in U.S. Pat. No. 3,832,363 that the epoxidation of an ethylenic compound to the corresponding oxirane compound is catalyzed by the presence of a boron oxide, a dehydrated boric acid and the hydrocarbyl esters thereof. The compounds disclosed in this patent which are useful as catalysts contain at least one B--O--B linkage.
The previously described catalysts suffer from one or more disadvantages when employed in liquid phase epoxidation. For example, many of the previously known catalysts materials are expensive and difficult to prepare and/or difficult to use, requiring special apparatus or highly selective reaction conditions and/or being limited to heterogeneous or homogeneous type reaction systems.
In coassigned copending U.S. patent application Ser. No. 565,004 filed Apr. 4, 1975, are disclosed binary and ternary boride compounds consisting of boron and at least one element selected from groups II-A, III-B, IV-B, V-B, VI-B, VII-B, VIII, III-A, IV-A and V-A of the Periodic Table, the rare earths and the actinides. No particular binders are disclosed in that application for forming shaped catalytic materials, but to carry out expoxidation using tubular reactor technology, it is necessary that the catalysts be shapes and not powders. However, certain binders can cause loss of catalytic activity.